Several attempts have been made to produce pregerminated seeds which give rise to consistently high and reproducible rates of germination in the field for many species of plants. However, such attempts have proven to be unsatisfactory since inter alia the storage life of such seeds is generally of limited duration or requires the employment of specialised storage facilities. Furthermore, pregerminated seed has not hitherto been considered amenable for sowing with conventional sowing methods and equipment i.a.because of the problem of seed dehydration under sowing conditions.
Granted patent specification EP 202879 B1, describes the obtention of high viability seed lots which are selected on the basis of having emerged radicles which have a moisture content at which radicle development is suspended without loss of seed viability. There is no suggestion that induction of desiccation tolerance in the radicle is advantageous and can lead to a product comprising germinated seeds which are capable of being stored at ambient temperatures for long periods of time without the need for specialised storage conditions. The high viability seed lots obtainable according to the disclosure of EP 202 879 B1 are not desiccation tolerant as indicated by several statements in said specification and as supported by the examples hereinafter demonstrating essential differences between the desiccation tolerant pregerminated seeds obtainable according to the teaching of this invention and the pregerminated seeds obtainable according to the conditions disclosed in EP 202 879 B1.
Many reports have appeared in the scientific literature of the effect upon seeds or seedlings of desiccation stress. One such report states that desiccation tolerance may be due to the presence of disaccharides such as sucrose and/or the presence of other plant sugars such as oligosaccharides. However, such a desiccation tolerance in the seed has been observed to be lost upon the emergence of the radicle from the seed coat and it is at this critical stage of germination that the ability to induce desiccation tolerance in the radicle has not hitherto been considered practicable [Koster K. L. and Leopold A. C. Plant Physiol. 88:829-832 (1988)].
Other workers have reported that maturing Barssica campestris seed acquire desiccation tolerance during seed development and that this has been observed to be concomitant with elevated levels of sucrose content. However, attempts at inducing desiccation tolerance in the emerged radicle of germinated seeds was neither described nor suggested [Leprince O. et al, Plant, Cell, and Environment 13:539-546 (1990)].
The art generally teaches of the loss of desiccation tolerance in germinated seeds. It has now surprisingly been found that desiccation tolerance can be induced in seeds having an emerged radicle. Furthermore, it has now been found that seeds comprising desiccation tolerant emerged radicles are capable of being sown without the need for employing refinements to sowing methods such as the application of encapsulating gels to pregerminated seed and the like. Surprisingly, seeds comprising desiccation tolerant emerged radicles as herein described are capable of being sown using conventional non-germinated seed sowing methods and equipment without substantial deleterious effect on seed viability.
Advantages of sowing seed in which the radicle has emerged include faster germination times once sown and provided that the seed supplier can guarantee a high seed viability per batch of seeds sown, a more reliable estimate of how much seed is required for sowing and hence more efficient growing methods.
One benefit of inducing desiccation tolerance in the emerged radicle of pregerminated seeds is that such seeds can be dried back to a moisture content approaching that of non-germinated seed. Thus, treated seed comprising desiccation tolerant emerged radicles is capable of being stored for long periods of time at ambient temperature i.e. without the need for employing specialised storage facilities such as refrigeration facilities and the like.
A further advantage is that seed comprising desiccation tolerant emerged radicles which have not been further dried back can be sown naked i.e. using conventional seed sowing methods and equipment without the need for employing encapsulating gels and the like.